This document provides guidance on improving yarn realization and controlling wastes in textile mills. It discusses calculating expected yarn realization based on factors like trash content and machine type. Norms for different types of wastes like blowroom droppings, card waste, comber noil, and yarn waste are provided. Measures to control process and reusable wastes are described. Maintaining invisible loss below 0.5% and usable waste below 5% is recommended. A 4-step approach is outlined to compare actual performance to expectations and address deviations through analysis and corrective actions.

1. How to improve Yarn
realization and control
wastes?
D.Shanmuganandam
Assistant Director
The South India Textile Research Association
Coimbatore – 641 014

2. How to improve Yarn realization and
control wastes?
D.Shanmuganandam
Assistant Director
The South India Textile Research Association
Coimbatore – 641 014
1. INTRODUCTION
In the production economics of a spinning mill, yarn realisation plays a significant
role. To illustrate, in the prevailing cotton cost and yarn selling price, even an 1%
improvement in yarn realisation would lead to a saving of Rs 20 lakhs per year for a
30000 spindle mill manufacturing 40s yarn.
Two decades ago, SITRA had brought out a publication on yarn realisation and
process waste control. During this intervening period, remarkable changes have taken
place in the industry with regard to technology of machinery, yarn quality and
workers’ efficiency. Keeping the above in mind, the formulae for estimating yarn
realisation and norms for different categories of wastes have been updated and
presented in this article.
This article also deals with various measures necessary to improve yarn realisation
and control wastes. Besides controlling process wastes such as blowroom and card
droppings, flat strips, comber noil, sweep waste and yarn waste, equal emphasis
should also be laid on the control of reusable wastes (soft waste) such as lap bits,
sliver bits, roving ends and pneumafil and roller waste. This is because, apart from
loss in production, reprocessing of soft wastes involves extra handling and
deteriorates yarn quality.
2. YARN REALISATION
Establishment of norms for wastes is a pre-requisite for a successful waste control in a
mill. Yarn realisation (YR) is largely governed by the level of trash in cotton,
expected yarn quality and type of machinery. Achievable yarn realisation can be
obtained using the following formulae:
A. For mills reusing the entire usable wastes in the same mixing
YR (%) = 97.5 – t – Wk – Wh for carded counts
Wc
= (100 – t – Wk) 1 – – Wh – 2.5 for combed counts
100

3. B. For mills not reusing the usable wastes in the same mixing
YR (%) = 97.5 – t – Wk – Wh – Wu for carded counts
Wc
= (100 – t – Wk) 1 – – Wh – Wu – 2.5 for combed counts
100
Where t = trash in mixing (%)
Wk = card waste (%)
Wc = comber noil (%)
Wh = yarn waste (%)
Wu = usable waste (%)
For example, for t = 3%, Wk = 7% and Wh = 0.5%, the expected yarn realisation is
87%. In the above case, if the mill produces combed yarn with a noil extraction of
18%, then the expected yarn realisation will be 70.8%. In both the cases, it is
assumed that the mill would reuse the usable wastes in the same mixing.
3. NORMS FOR WASTES
Norms for different categories of wastes are summarised in Tables 1 and 2.
Table 1 Norms for process waste and invisible loss
Type of waste Norms (%)
Blow room droppings Same as trash in cotton
Gutter/filter waste 1.0
Card waste (modern cards) 20s - 40s : 7.0
Above 40s : 6.0
Sweep wastea 1.0
Yarn waste
Conventional cone winding 0.1
Doubler winding 0.1
Ring doubling 0.1
TFO twisting 0.1
Auto winding
- with magazine feed 0.5
- with auto feed 0.8
Invisible loss 0.5
‘a’ includes suction fan wastes of draw frames, fly frames and humidification plant.
Table 2 Norms for usable waste (%)
Type of waste Lap feed Chute feed
Lap bits and card web 0.7 0.2
Sliver waste in drawing and fly frames 0.5 0.5
Waste at comber preparatory and combers 1.0 1.0
Roving ends 0.3 0.3
Pneumafil and roller waste (ring frames) 2.5 2.5
Total 5.0 4.5

4. For the method of consolidating waste, estimating invisible loss and checking the
accuracy of figures, reference may be made to SITRA monograph “Quality Control in
Spinning”, 1998.
4. PROCESS WASTE
4.1. Blow room
Amount of waste extracted in blow room is mostly determined by the trash level in
cotton. In modern blow room lines, greater importance is attached to the opening of
cotton than cleaning. Hence, cleaning efficiency of about 60% in cottons with high
trash content and 50% in cottons with low trash level can be considered to be quite
satisfactory in these lines. For good cleaning efficiency, the waste extracted in blow
room should be about the same as the trash in mixing. If, however, the cleaning
efficiency achieved is less than 50% – 60%, then the total waste extracted should also
be low. It should be ensured that the overall lint in waste is no more than 40% in
cottons with high amount of trash and 50% for cottons with low level of trash.
The expected lint loss can be estimated using the following formula:
(t – t L) 100
Wb = ……………… (1)
(100 – L)
(t – t L)
∴ L = 100 1 – ……………… (2)
Wb
Where
t = trash in mixing (%)
tL = trash in lap (%)
Wb = waste extracted in blow room (%)
L = % lint in waste
Illustrative Examples
1. Trash in mixing : 3.5%
Trash in lap : 1.5%
Waste extracted : 3.2%
Calculate the lint loss in waste.
Refer equation (2),
(t – t L)
Lint loss (L) = 100 1–
Wb
(3.5 –1.5)
= 100 1–
3.2
= 38%
2) Trash in mixing : 5%
Trash in lap : 2%
Expected lint loss : 40%
Estimate the amount of waste to be extracted in blow room

5. Refer equation (1),
(5 – 2) x 100
Wb =
(100 – 40)
= 5%
Presently, many mills are using Automatic Waste Evacuation System (AWES)
in blow room, cards and combers, which removes wastes from these machines either
continuously or intermittently. This system not only reduces the man power required
to collect and transport wastes but also helps to control the incidence of fly and fluff
generation in these departments and improves yarn quality, particularly short thick
faults.
In mills not equipped with filters in blow room, a proper estimate of gutter
waste should be made, since gutter cleaning is not done regularly at the end of every
month. The estimate of gutter waste could be made based on the quantum of waste
collected and number of days the blow room has worked.
4.2. Cards
Waste extracted in cards is usually in the range of 4% to 7% depending upon
the type of card and mixings. Between same type of cards and mixing, the waste %
should not vary more than ±0.5% from the average. The card waste is also governed
by the cleaning efficiency achieved in blow room. Thus, while assessing the waste,
combined waste extracted in blow room and cards should be taken into account. The
combined cleaning efficiency will be generally in the range of 90% to 98% with
modern cards. To illustrate, for 4% trash in cotton and 0.12% trash in sliver, the
combined cleaning efficiency is 97%.
4.3. Combers
Generally, all cottons respond well to combing for noil extraction up to 16%. For levels
beyond 16%, the law of diminishing returns operates and the improvement in yarn
quality is not commensurate with the additional cost of production. Higher levels of
waste should be extracted only in such cottons where combing performance is
satisfactory or where the end use requires yarns of very high quality. Under good
working, for every 1% increase in comber waste, yarn lea strength will increase by 1%
and evenness is expected to improve by 0.15 U%. Variation in noil % between
combers must be maintained within ±0.5% and between heads it must be within ±1.5%.
4.4. Yarn waste
Yarn waste in a spinning mill should not normally exceed 0.1% with
conventional cone winding. In the case of automatic cone winding, the yarn waste
generally varies from 0.5% in winders fitted with magazine feed to 0.8% in winders
with auto bobbin feed system. However, if the yarn under goes additional processes in
post spinning such as reeling, doubler winding and TFO twisting/ring twisting, the
waste would be somewhat higher. A high incidence of yarn waste, apart from leading
to a loss of Rs 6 to Rs 15 per spindle per year for every 0.1% waste, is an indication of
poor machinery condition and maintenance, and inappropriate work practices of
operatives. A number of factors such as vibrating spindles, spindles out of center, soft
cops, oil stain on yarn, improperly built cop bottom, yarn left over in cops during
winding and operatives using excess length while piecing, leads to high yarn waste. For
further information on yarn waste control, reference may be made to SITRA publication
“Measures to Control Hard Waste in Spinning” Vol.41, No.11, March 1996.

6. 4.5. Sweep waste
Sweep waste in all the departments of a spinning mill together should be
within 1%. A high sweep waste arises invariably due to operatives throwing away the
wastes like roller waste, lap bits, sliver bits, roving ends, etc. on the floor and
generation of fly and fluff. The fly frame and ring frame tenters should be provided
with hip bags and it should be ensured that the roller waste and roving ends are
deposited in the bags after piecing the broken ends. Good waste, if any, should be
picked before sweeping instead of sorting out the waste later. A high price fetched for
sweep waste would give an indication of the presence of good fibers in the waste.
5. INVISIBLE LOSS
Invisible loss in a spinning mill occurs due to a number of factors such as
short fibers (fluff) escaping from the departments, improper accounting of wastes
produced, weighment errors in cotton purchased and wastes sold, excess give away of
yarn and inaccuracies in the estimates of stock held in process. Since it would be
difficult to accurately assess the process stock, it is suggested that the invisible loss be
assessed only once in 4 months for control purposes. This will help in minimising the
variation in invisible loss due to errors in process stock estimate. From the data
compiled every month, a cumulative average could also be taken for control purpose.
However, not much importance should be given for estimates made from data less
than 4 months.
To maintain the invisible loss within 0.5%, mill should also ensure that
moisture content in the finished goods is at par with the level prevailed in cotton at the
time of purchase. For more details on invisible loss control, reference may be made
to SITRA Focus “How to Control Invisible Loss in Spinning Mills? – Case study”,
Vol.23, No.3, September 2005.
6. USABLE WASTE
By exercising good control over
end breaks in various machines
material handling and storage and
work practices of operatives
a mill could maintain the usable waste below 5%.
7. CONCLUSION
In many mills, there is good scope for improving yarn realisation and reducing
wastes (as revealed by inter-mill studies as well as consultancy studies by SITRA).
The following 4 steps would be helpful to improve yarn realisation.
Step 1: Calculate actual yarn realisation and different categories of wastes
Step 2: Using the formulae given in this article, estimate the expected yarn
realisation for the existing working conditions.
Step 3: Compare the actual yarn realisation with the expected value and actual
wastes with norms.
Step 4: Analyse the causes for deviation and initiate corrective action. Create
awareness among the workers and technical staff about the importance
of waste control. Good supervision and proper maintenance of
machinery would help to reduce the waste.
Source: The south Indian Textile Research Association, Coimbatore-641014, India,
http://www.sitra.org.in/default.aspx.
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